Browsing by Subject "Cycloaddition"

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    5-Alkenylthiazoles as In-Out Dienes in Polar [4+2] Cycloaddition Reactions
    (Wiley, 2013-09-25) Alajarín, Mateo; Cabrera, Jose; Sanchez-Andrada, Pilar; Bautista, Delia; Pastor Vivero, Aurelia; Química Orgánica
    5-Alkenyl-2-aminothiazoles react as in-out dienes with a wide range of electron-poor dienophiles leading to the corresponding cycloaddition products in good to excellent yields. The [4+2] cycloadditions of 5-alkenyl-2-aminothiazoles can be classified as site-selective since only the diene moiety including the formal C-C double bond of the heterocycle and that of the side-chain is involved. Calculations of the HOMO energy values of representative 5-alkenyl-2-aminothiazoles are disclosed The cycloadditions are endo-selective with N-phenylmaleimide or maleic anhydride and regioselective when the reactions are conducted with non symmetrical dienophiles. Completely oxidized cycloadducts are obtained in the reactions of 5-alkenyl-2-aminothiazoles with naphthoquinone or DMAD. Unexpectedly, the reactions with PTAD are not stereospecific. A mechanism placed at the concerted/stepwise boundary is proposed.